The present invention relates to ink jet printing, and more particularly to novel electrode patterns for piezo-electric ink jet print heads.
When an electric field is applied to a piezo-electric material or composite, it changes its dimensions. In piezo-electric drop-on-demand ink jet printing, actuation can occur when a thin wall of an ink chamber is deformed through the use of a piezo-electric transducer or actuator causing a change in pressure in the chamber and leading to the formation and ejection of a drop out of a small orifice hole.
One of the difficulties to date in achieving high resolution piezo-electric printheads, is how to limit the size of printhead. Printhead size is directly related to the size of the piezo-electric transducer. To achieve sufficient ink displacement, relatively large transducers are needed. This, however, is in contrast with the necessity for large numbers of transducers in a relatively small area to achieve the required print quality and density (i.e., resolution).
Another difficulty is in designing print actuators that provide sufficient displacement So eject an ink drop at a reasonable application voltage.
One approach that has been employed in an effort to address the foregoing difficulties is by attaching one end of a piezo-electric rod or other structure to a thin deformable membrane making up a wall of the ink chamber. When an electrical signal is applied, the piezo-electric material is energized in xe2x80x9cdirect modexe2x80x9d causing it to expand and push on the membrane creating a volume change in the chamber. This volume change in the chamber results in the formation of an ink drop which is then ejected through the orifice hole and onto a page.
There are two principal types of direct modes. The first is commonly referred to as xe2x80x9cD31 mode.xe2x80x9d In D31 mode, the direction of deformation of the piezo-electric transducer is perpendicular to the polarization of the piezo-electric material and to the applied electric field. In general, piezo-electric transducers that operate in D31 mode are arranged parallel to each other in an array, with electrodes placed between each individual transducer. While the displacement per unit voltage applied for each individual transducer is relatively large, the total displacement of the ink chamber membrane is limited to the amount of displacement of each individual transducer. In other words, the displacements of the individual transducers are parallel to each other and there is no cumulative displacement. As a result, a large number of individual transducer elements and a correspondingly large printhead are necessary to achieve high resolution printing.
An alternate direct mode is commonly referred to as xe2x80x9cD33 mode.xe2x80x9d In D33 mode, the direction of deformation of the piezo-electric transducer is parallel to both the polarization of the piezo-electric material and electric field applied. In D33 mode it is possible to stack piezo-electric layers with a cumulative displacement.
One difficulty with D33 mode is how to precisely control individual print actuators to effect drop on demand printing. To control the actuators, it is necessary to connect them to a control signal. Where the actuator electrodes reside on an exposed external surface, access is relatively simple. However, to achieve high resolution it is necessary to arrange multiple actuators in a closely spaced array. In such an arrangement it often is difficult to access the internal electrodes. Thus, where even two parallel columns of actuators are used there are at least two internal electrode surfaces that are not readily accessible.
Accordingly, there is a need for a piezo-electric printhead that provides high resolution printing in a small or compact assembly. Desirably, such a piezo-electric printhead is configured with electrodes that permit ready access (i.e., connection) for controlling the printhead operation.
There is a further need for a method for making a piezo-electric printhead that facilitates readily fabricating such a printhead in which a large number of transducers are contained within a limited area such that print high print resolution requirements are readily achieved.
A piezo-electric printhead includes a first piezo-electric actuator disposed parallel to a second piezo-electric actuator, the first and second actuators having a shared inner electrode disposed between them. A first control electrode is disposed on an outside surface of the first piezo-electric actuator and a second control electrode disposed on an outside surface of the second piezo-electric actuator.
The piezo-electric actuator is fabricated from a single ceramic block, having a ceramic base disposed beneath a multilayer structure with alternating piezo-electric and conductive layers. A positively charged electrode is disposed on a first face of the piezo-electric actuator and a negatively charged electrode is disposed on a second face of the piezo-electric actuator. In one embodiment, control circuitry is connected to the electrodes through conductive vias in the base of the block.
The present invention also contemplates a method of manufacturing a piezo-electric printhead. Such a method includes the steps of providing a block having a piezo-electric layer disposed on a ceramic base, with the piezo-electric layer having electrodes embedded therein in the form of a metal paste. The piezo-electric layer is diced to form a first column of piezo-electric actuators, and a second column of piezo-electric actuators disposed adjacent to the first column in a parallel array. Each column has an internal face and an outer face. A shared electrode is formed on the internal face and an oppositely charged electrode is formed on the outer face, with the shared electrode acting as a ground and the oppositely charged electrodes connected to a control circuit. An outer surface of the piezo-electric layer is plated with conductive material. The ceramic block is cut into an array of piezo-electric actuators.
In a preferred embodiment, the conductive layers are disposed in at least two distinct, alternating patterns. A first pattern is disposed to define at least a first gap at a first longitudinal position. A second pattern is disposed to form at least a second gap at a second longitudinal position different from the first longitudinal position. The conductive layers of the first pattern are electrically connected to the first control electrode and the conductive layers of the second pattern are electrically connected to the second control electrode.
The present invention also contemplates a method of fabricating a piezo-electric printhead that includes the steps of providing a ceramic block having a ceramic base disposed beneath a layered piezo-electric structure with a conductive layers embedded between successive piezo-electric layers and cutting the piezo-electric structure to expose the conductive layers. The piezo-electric structure is plated to form a first electrode and a second electrode in contact with the conductive layers. The method includes dicing the piezo-electric structure to form an array of individual actuators and cutting conductive vias into the base of the block. Control circuitry is connected to the electrodes through the conductive vias.
In a preferred method, a first dice is formed in the piezo-electric layer to a first predetermined depth and a second dice is formed dice in the piezo-electric layer parallel to the first dice. The second dice is formed to a second predetermined depth different from the first predetermined depth. The first and second dice define a column of piezo-electric actuators. The actuator column has an internal face and an outer face, with a shared electrode on the internal face and an oppositely charged electrode on the outer face.
The method further includes plating an outer surface of the piezo-electric layer with conductive material and cutting the ceramic block transverse to the dicing to a third predetermined depth between the first and second predetermined depths forming an array of piezo-electric actuators.
The present invention further contemplates a method of controlling a piezo-electric actuator that includes the steps of connecting control circuitry to a piezo-electric actuator through a conductive via disposed beneath the actuator and supplying a signal from the control circuitry to the piezo-electric actuator. The signal travels through the conductive via to a control electrode in contact with the actuator.